Help: slip-on tub spout

I'm working on installing a new tub and shower faucet set. I had someone doing some work for me while I was away, but he left it partially unfinished. My question is related to the slip-on tub spout and the white plastic adapter that fits it to the 1/2" copper pipe protruding from the shower wall.

When I returned from being away, I noticed that the tub spout hadn't been caulked. So, I backed off the set screw and pulled the spout off to clean everything up. When I pulled the spout off, I found a white plastic adapter with two o-rings. Trouble is, one of the o-rings fell off mid-pull and now I don't know what goes where. (I know, it's probably something simple ...)

Here's a picture of the white adapter on the wall with the one o-ring still intact:

The o-ring on the adapter is 1" in diameter. The o-ring that fell off mid-pull is 7/8" in diameter. I tried re-installing the tub spout without the second o-ring but there's a small leak at the wall (the setscrew was tight, etc.).

Here's an internal picture of the tub spout:

Can someone help me figure this out? I'm not even sure if this so-called adapter came with the tub and shower faucet set or if it's something that was added by the guy who helped me (he's now away on vacation and I can't contact him). Is there a name for the white adapter?

This is just a guess, since that adapter is not usually removed from the spout. You must have unscrewed the allen bolt too far. But that washer probably sits in the end of the adapter, around the copper tubing, but if so, your copper stub may be too short to make a good seal. Try sliding the adapter off the copper stub, put the "O" ring in the recess on the end, put the adapter into the spout tightly, insert the clamping screw most of the way, and then slide it onto the copper, before tightening it the last bit.

Thanks for this. I will be working on it again tomorrow and see what happens. I am glad that you said that the adapter isn't normally separated from spout like that. However, the adapter seems to be "stuck" on the tubing pretty good. I think there is some scoring ... just enough to make sliding it off a chore. I'll get to the bottom of this one way or another.